JP5532969B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device and an image forming apparatus, and more particularly to a mixing mechanism of a replenishing toner and a developer in a two-component developer.

  In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a printing machine, an electrostatic latent image formed on a photosensitive member as a latent image carrier is subjected to visible image processing by a developing device, and the visible image is converted into a sheet. A recording output can be obtained by transferring to the above.

As a developer used for development, there is a two-component developer obtained by mixing a toner and a carrier in addition to a one-component developer containing only a magnetic or non-magnetic toner.
The two-component developer is composed of a toner and a carrier that carries the toner, and the toner can be electrostatically attracted to the electrostatic latent image on the photosensitive member by charging the toner by a frictional charging effect that occurs during stirring and mixing. It is said.

  The developing device includes a developing sleeve for supplying a developer toward the electrostatic latent image on the photosensitive member by causing the developer to rise on the peripheral surface by magnetic force, and an agitation for supplying the developer mixed with stirring to the developing sleeve. A configuration including a sleeve is known, and a developer in which toner is consumed for visible image processing of an electrostatic latent image on a photoreceptor is collected by a developing device.

On the other hand, the two-component developer is stirred and mixed in the developing tank, and the toner is charged at that time. However, if the charge amount is not sufficient, the image density is affected and the image quality may not be stabilized. .
In particular, when the charge amount is less than or equal to a predetermined amount, not only the image density cannot be maintained at a predetermined density, but also toner adhesion to the background surface of the photosensitive member, which is called background stain, due to the generation of floating toner occurs. Further, when the charge amount is a predetermined amount or more, image fogging due to a large amount of toner adhering to the image occurs.

  Therefore, as a means for solving such a problem, a circulation means provided with a configuration in which a stirring unit is provided at a position different from the developing device and new toner is supplied into the developer using air. A configuration has been proposed in which the developing unit and the agitation unit are connected, the agitation unit performs agitation according to the state of the developer, and a developer whose toner density and charge amount are appropriately adjusted is supplied to the development unit (for example, Patent Document 1).

When toner is replenished to the developer in the agitation section using air, if the toner dropped from the replenishment toner container toward the replenishment path is agglomerated (aggregated), It takes time until the toner is completely dispersed in the developer in the stirring unit.
Therefore, it is necessary to set various conditions of the stirring unit in advance assuming such a state. For example, the capacity of the stirring unit is increased, the rotation speed of the stirring member is increased, and the number of stirring members is increased.
However, if the capacity is increased, the size of the apparatus increases, and the increase in the number of rotations of the stirring member and the increase in the stirring member increase damage due to an increase in mechanical stress on the developer, resulting in deterioration of the developer. It can also be early.

  An object of the present invention is to improve the dispersibility between a developer and a toner without causing deterioration due to stress in a short time in view of the problems in the above-described conventional developing devices, particularly problems during stirring. A second object is to provide a developing device and an image forming apparatus each having a configuration capable of improving the charging performance of the replenishing toner.

In order to achieve the above object, the present invention comprises the following arrangement.
(1) A developing unit that performs a visible image processing on the electrostatic latent image formed on the latent image carrier with a developer composed of toner and a carrier, and the developer collected from the developing unit is developed again in the developing unit. A circulation unit that transports the developer toward the developer supply unit. The circulation unit is provided with a storage unit that stores a part of the developer at a position before reaching the development unit, and the recovery unit is configured to collect the recovery unit in the storage unit. In a developing device provided with a stirring member that stirs and mixes the developer and newly supplied toner,
In addition to the developer flow path leading to the circulation path, the developing unit is provided with a replenishment toner mixing conveyance path connected to a replenishment toner conveyance path that conveys replenishment toner to the circulation path by an air flow . A developing device characterized in that the replenishment toner and the developer from the developing unit are mixed in the replenishing toner conveyance path and conveyed to the accommodating portion of the circulation unit.

( 2 ) In the developing device according to (1),
Wherein the conveying speed of the toner in the replenishment toner transport path, using the ratio between the air and the toner powder, that toner powder is set the speed air flow that is obtained in less state as compared to air A developing device.

(3) In the developing device according to (1) or (2) ,
The replenishment toner conveyance path has a conveyance path length from a position where the air flow conveyance of the replenishment toner starts to a position where the developer conveyed from the developing unit joins, and the replenishment toner can be sufficiently dispersed in the air. A developing device characterized in that a distance is set.

( 4 ) In the developing device according to one of (1) to ( 3 ),
Examples air velocity in the supply toner carrying path, using the ratio between the air and the developer, a developing device a developer, characterized in that the air flow rate of less state as compared to air is set resulting that speed .

( 5 ) In the developing device according to one of (1) to ( 4 ),
The distance through which the developer can be sufficiently dispersed in the air is set as the length of the conveyance path from the position where the developer and the replenishment toner from the developing unit are joined by the air flow to the accommodation unit of the circulation unit. A developing device.

( 6 ) An image forming apparatus using the developing device according to any one of (1) to ( 5 ).

  According to the present invention, in addition to the developer conveyance path from the developing section to the circulation section, the replenishment toner mixing conveyance path connected to the replenishment toner conveyance path through which the replenishment toner is conveyed is provided. A state in which replenishment toner is mixed with the developer is obtained. Thus, unlike the case where the replenishment toner is agitated by the agitating member, the developer in the premixed state is agitated, so that the agitation efficiency and the charging efficiency can be improved.

  In particular, the replenishment toner or developer has a transfer speed and a transfer distance which are increased in dispersibility in the air until reaching the merging position with the developer conveyed from the developing unit or reaching the circulation unit. Since the sheet is conveyed according to the set conditions that can be increased, the mixing property with the developer is improved.

1 is a cross-sectional view illustrating a configuration of an image forming apparatus using a developing device according to an embodiment of the present invention. FIG. 2 is a diagram for explaining a configuration of an entire toner supply mechanism including the developing device shown in FIG. 1. FIG. 2 is a schematic diagram illustrating a main configuration of a developing device according to an embodiment of the present invention. It is a figure for demonstrating the structure used as the characterizing part of this invention. FIG. 5 is a diagram for describing a conveyance state in a replenishment toner conveyance path used for the characteristic portion illustrated in FIG. 4.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 shows an image forming apparatus using a developing device according to the present invention. The image forming apparatus shown in FIG. 1 is a tandem full-color printer. However, the present invention is not limited to this, and can be applied to a copying machine, a facsimile machine, and the like.
In the image forming apparatus shown in FIG. 1, each color (yellow, magenta, cyan, black) faces the lower surface of an intermediate transfer belt 10A as an unfixed image carrier provided in the intermediate transfer unit 10 in the apparatus main body 100. ) Corresponding to the image forming units 6Y, 6M, 6C, and 6K.

These image forming units 6Y, 6M, 6C, and 6K have the same structure except that the color of the toner used in the image forming process is different. In the following description, only the numerical symbols common to the image forming units will be described, and the alphabetic symbols indicating the toner colors will be omitted.
Each image forming unit 6 includes a photosensitive drum 1 as a latent image carrier, a charging unit 2, a developing device 3, a cleaning unit 4 and the like disposed around the photosensitive drum 1.
An image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on the photosensitive drum 1, and a desired toner image is formed on the photosensitive drum 1.
The photosensitive drum 1 is rotationally driven in the clockwise direction in the drawing by a driving unit (not shown), and the surface is uniformly charged at the position of the charging means 2 (charging process).

The surface of the photosensitive drum 1 reaches an irradiation position of a laser beam emitted from an exposure unit (not shown), and an electrostatic latent image is formed by exposure scanning at this position (exposure process). When the position reaches this position, the visible image is processed with the toner contained in the developer supplied therefrom, and the development process is executed.
The surface of the photosensitive drum 1 carrying the toner image that has been subjected to the visible image processing in the development process reaches a position facing the intermediate transfer belt 10A and the primary transfer bias roller 5, and at this position on the photosensitive drum 1. The toner image is transferred onto the intermediate transfer belt 10A (primary transfer step).

After the transfer, the surface of the photosensitive member 1 reaches a position facing the cleaning unit 4, and untransferred toner remaining on the photosensitive drum 1 is collected at this position (cleaning step). After cleaning, the potential of the surface of the photosensitive drum 1 is initialized by a neutralizing roller (not shown). By passing through such steps, a series of image forming processes performed on the photosensitive drum 1 is completed.
The image forming process described above is performed at the time of forming a single image of only a monochrome image and at the time of forming a full color image. Each step is performed. That is, a laser beam based on image information from an exposure unit (optical writing device) (not shown) disposed below the image forming unit is applied to the photosensitive drums of the image forming units 6Y, 6M, 6C, and 6K. Irradiated toward. Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are transferred onto the intermediate transfer belt 10A in an overlapping manner. Thus, a color image is formed on the intermediate transfer belt 10A.

The four primary transfer bias rollers 5Y, 5M, 5C, and 5K respectively sandwich the intermediate transfer belt 10A with the photosensitive drums 1Y, 1M, 1C, and 1K to form a primary transfer nip. The primary transfer bias rollers 5Y, 5M, 5C, and 5K are applied with a transfer bias having a polarity opposite to the polarity of the toner.
The intermediate transfer belt 10A travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 5Y, 5M, 5C, and 5K. Thus, the toner images of the respective colors on the photosensitive drums 1Y, 1M, 1C, and 1K are primarily transferred while being superimposed on the intermediate transfer belt 10A.
The intermediate transfer belt 10A onto which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 7 as a secondary transfer unit. The color toner image formed on the intermediate transfer belt 10A is collectively transferred onto a transfer sheet P as a recording medium conveyed to the secondary transfer nip position.

A plurality of transfer sheets P are stored in a paper supply unit 8 disposed in the lower part of the apparatus main body 100, and are separated and fed one by one by a paper supply roller 9. The fed transfer paper P is temporarily stopped by the registration roller pair 10, and after the oblique deviation is corrected, it is conveyed toward the secondary transfer nip by the registration roller pair 10 at a predetermined timing. As described above, a desired color image is transferred onto the transfer paper P at the secondary transfer nip.
The transfer paper P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the fixing unit 11 where the color image transferred to the surface is fixed by heat and pressure generated by the fixing roller and the pressure roller. The
After the fixing, the transfer sheet P is discharged as an output image to the paper discharge unit 100A formed on the upper surface of the apparatus main body 100 by the paper discharge roller pair 12 and stacked. Thus, a series of image forming processes in the image forming apparatus is completed. In FIG. 1, reference numeral 13 denotes a cleaning device for the intermediate transfer belt 10A.

FIG. 2 is a diagram illustrating a configuration of the entire toner supply mechanism including the developing device.
In FIG. 2, the developing device will be described in detail later. A developing unit that executes a developing process with a two-component developer in which a carrier and a toner are mixed with a photosensitive drum, and a developer collected from the developing unit. A circulation unit that transports the developer again toward the developer supply unit of the development unit is provided.

  In FIG. 2, the developing device 3 includes a developing tank 30 that can store a developer for developing the electrostatic latent image on the photosensitive drum 1, a developer collected from the developing tank 30 at a position away from the developing tank 30, and A developer container 40 that stirs and mixes new toner that matches the consumed toner, a toner supply part 60 that replenishes new toner toward the developer container 40, and agitated and mixed after being discharged from the developer container 40 A rotary feeder 50 for transferring the developer and an air pump 51 corresponding to a developer circulation drive source for transferring the developer toward the developing tank 30 by air pressure are provided as main parts. In FIG. 2, the developing tank 30 is configured in a cartridge shape.

The developer tank 30 and the developer container 40 are connected by a developer recovery path 41 and a rotary feeder 50 connected from the inside of the developer tank 30 and a developer supply channel 42 connected to the upper part of the developer tank 30. Thus, a developer circulation path is constructed, and a circulation section including members provided in the circulation path is constructed.
As will be described with reference to FIG. 3, the developer supply channel 42 connected to the developing tank 30 is connected to face one end in the axial direction of the transport screw 32. Further, the developer recovery channel 41 is connected to correspond to the side to which the developer supply channel 42 is connected in the axial direction of the other conveying screw provided in the developing tank 30.
The developer accommodating portion 40 has an appearance like a silo with an upper portion being cylindrical and a lower portion having a downward conical shape, and a stirring member described in detail in FIG. 4 is provided inside.

A drive motor 40A and a reduction gear group (in FIG. 2, the gear groups are collectively indicated by reference numeral 40B) are provided above the developer accommodating section 40.
The developer agitated and mixed in the developer container 40 is fed to a rotary feeder 50 that is provided with a paddle that can adjust the supply amount and is driven to rotate by a drive motor 50A, and the supply amount is adjusted at this position. The developer is conveyed toward the developing tank 30 by the air flow generated by the air pump 51.

  The toner supply unit 60 air-conveys the toner tank 61, the replenishment toner conveyance path 62 connected between the toner tank 61 and the developer container 40, and the toner replenished in the replenishment toner conveyance path 62. Air pump 63 for

FIG. 3 shows the internal structure of the developing tank 30 used in the developing device 3.
In FIG. 3, in the developing tank 30, a developing sleeve 31 that bears a developer facing the photosensitive drum 1, and a conveying screw that is disposed in the vicinity of the developing sleeve 31 and has an opposite lead direction set. 32 and 33, and a doctor blade 34 for defining the developer carrying amount on the surface of the developing sleeve 31 are provided.
The developer in the developing tank 30 is transported from the front side to the back side in the drawing by the transport screws 32 and 33, and when a part of the developer is sucked and adsorbed by the magnetic force in the developing sleeve 31, the developer blade is evenly distributed. After being smoothed, the electrostatic latent image on the photosensitive drum 1 is developed with toner by contacting the photosensitive drum 1 to form a toner image.

The developed developer is conveyed to the developer accommodating portion 40 from the developer recovery channel 41 (see FIG. 2) connected to the end of the conveying screw 33.
A toner density detecting means (not shown) is installed on the most downstream side of the conveying screw 33, and new toner is replenished from the toner tank 61 based on the signal. As described above, the toner is replenished by airflow conveyance by the air pump 63 connected to the replenishment toner conveyance path 62.

In FIG. 4, the developer accommodating portion 40 uses a silo-shaped container 43 having a cylindrical shape at the top and a funnel-like shape with a vertical cross-section of a downward cone, and is located at the bottom and has the smallest diameter. The discharge port 400 communicates with the rotary feeder 50.
In the internal space of the developer accommodating portion 40, a screw 44A that is integrated with a rotating shaft 44 that is suspended from the motor 40A as a stirring member and moves the developer in the direction opposite to the flow direction of the developer, and a rotation A stirring blade 45A having an end plate 45 that can be interlocked with the output gear of the reduction gear group 40B driven by the shaft 44 is provided.
The stirring blade 45A has a configuration in which a plurality of slits are formed in a plate-like member passing through the rotation center of the end plate 45 and parallel to the radial direction, and the remaining developer is pushed and stirred while passing a part of the developer. Is used.

In the configuration shown in FIG. 4, the outer diameter of the screw 44A is set to 18 mm, the inner diameter of the container 43 of the developer container 40 is set to 20 mm, and the inner diameter of the developer recovery path 41 in the developing unit is set to 12 to 18 mm.
The rotary feeder 50 connected to the discharge port 400 located at the bottom of the container 43 is provided to control the developer discharge amount in accordance with the rotation amount of the motor 50A (see FIG. 2). A rotary valve member 50B having a plurality of blades 50B1 that are fixed to the rotation shaft of 50A and extend radially is provided.

The features of the present invention will be described below with the above configuration as an object.
A feature of the present invention is that, in addition to the developer recovery path 41 reaching the container 43 of the developer accommodating section 40 in the developing section, a replenishment toner mixing transport path 64 extending from the developing tank 30 to the replenishment toner transport path 62 is provided. The toner supplied to the developer from the developing unit is preliminarily mixed and reaches the stirring unit in the container 43.

FIG. 4 is a diagram for explaining the above-described features, and shows a state in which the configuration shown in FIG. 2 is developed.
In FIG. 4, the replenishing toner mixing and transporting connected to the developing unit in the replenishing toner transporting path 62 at a position before reaching the developer containing part 40, separately from the developer recovery path 41 connected to the developing tank 30. A path 64 is provided.
To the replenishment toner conveyance path 52 where the replenishment toner mixing conveyance path 64 merges at the merge position P2, a toner tank 61 storing replenishment toner is connected at the merge position P1.

The toner tank 61 has a cylindrical shape at the top and a funnel shape with a longitudinal cross-section of a downward cone. The toner tank 61 is configured by a container capable of dropping a new toner contained therein by its own weight. A supply roller 65 is provided on the front side of the joining position P1.
The replenishing roller 65 has a concave pocket 65 </ b> A capable of storing toner in a part of the peripheral surface. The supply roller 65 is configured to regulate the supply amount of toner to be supplied by setting the size of the concave pocket 65A and the rotational speed.
When the toner supplied by the replenishing roller 65 reaches the merging portion P1 of the replenishing toner conveyance path 62, the toner is conveyed in an airflow toward the developer accommodating portion 40 included in the circulation portion according to the flow of air supplied from the air pump 63. . In the configuration shown in FIG. 4, the inner diameter of the replenishment toner conveyance path 64 is set to 1 to 3 mm.

Since the present embodiment is configured as described above, a part of the developer conveyed toward the developer storage unit 40 of the circulation unit is supplied and replenished toner mixed and conveyed separately from the developer recovery channel 41 The replenishment toner conveyance path 62 is reached via the path 64.
In the replenishment toner conveyance path 62, the replenishment toner and the developer conveyed in the airflow are mixed in advance before reaching the developer accommodation unit 40 in the circulation unit, and the so-called premix developer is incorporated in the developer accommodation unit 40. be introduced.

  As described above, since the replenishment toner is mixed with a part of the developer, unlike the case where the developer and the replenishment toner are newly mixed and stirred in the developer container 40, the replenishment toner is changed to a predetermined mixing ratio. The stirring time can be shortened and the stirring efficiency can be improved. Thereby, since the rotation speed in the member used for stirring can be lowered, it is possible to reduce the stress on the developer generated during the stirring. In addition, since the developer mixed with the replenished toner in advance can be a target to be stirred, a predetermined stirring and mixing ratio can be obtained even if the capacity of the stirring portion is reduced.

In this embodiment, since the replenishment toner is conveyed by airflow conveyance and mixed with a part of the developer, the configuration of the airflow conveyance path is appropriately selected, unlike the case where the toner is conveyed using a screw member. In addition, the installation position of the toner tank 61 can be arbitrarily set with respect to the installation position of the stirring unit and the development unit.
Further, when the replenishment toner moving in the replenishment toner conveyance path 62 comes into contact with the carrier in the developer at the joining position P <b> 2 of the replenishment toner mixing conveyance path 64, it is between the developer introduced from the replenishment toner mixing conveyance path 64. Because of the difference in the transport speed due to the difference in specific gravity, a frictional charging effect by frictional contact can be obtained.
As a method for improving the triboelectric charging property, it is conceivable to increase the rotation speed of the stirring member in the stirring unit. However, this method causes an increase in stress on the developer. In the present invention, the charging characteristics can be improved without increasing the stress on the developer.

Next, another feature of the present invention will be described.
Another feature of the present invention is that the toner mixing property with the developer is improved by enhancing the dispersibility of the replenishment toner or developer in the air. In other words, the mixing property and the triboelectric charging characteristic are improved by increasing the contact probability of the toner or developer in a separated state.

As a method for obtaining this feature, (1) setting of the airflow conveyance speed of the replenishing toner or developer, and (2) setting of the airflow conveyance path length can be mentioned.
In the method described in (1), the airflow conveyance speed (air flow rate) in the replenishment toner conveyance path 62 and the mixing ratio (mixing ratio) of toner in the air are from the dispersed state shown in FIG. The above-described air flow rate (flow rate) is determined so as to obtain the dispersion state shown in FIG. The flow rate in this case is a parameter that affects the mixing ratio. As a result, the air velocity is high (the air flow rate is large) and the mixing ratio is small (the amount of powder is small compared to the amount of air), so that the probability of toner contact with the developer is increased and the mixing rate is improved. Will be. In other words, a large amount of powder toner is dispersed in the air rather than a state where toner lumps are intensively biased.

In the method described in (2), the replenishment toner introduced from the toner tank 61 to the replenishment toner conveyance path 62 can be broken down into a powder form by removing the lump form, specifically, FIG. 4, the length from the joining position P1 with the toner tank 51 to the joining position P2 with the replenishing toner mixing and conveying path 64, which is the position where the developer from the developing unit is introduced, as indicated by the symbol L1, or As indicated by reference numeral L2, the length from the joining position P2 to the developer accommodating portion 40 is defined.
In this method, even when the flow velocity of air when being conveyed is set to the conditions listed in (1), if the blocky toner or developer cannot be broken, Since it breaks down due to rubbing with the inner surface of the conveyance path that occurs when moving along the flow, it can be made into a powdered state to increase the probability of mutual contact.

  In the above characteristics, the dispersibility can be improved by disintegrating and agglomerating the toner and developer that are aggregated into a lump, and the mixing ratio is increased.

  In the embodiment described above, replenishment of new toner from the toner tank 61 is executed based on a signal from a toner density sensor provided in the developing unit. For this reason, when no new toner is replenished, the mixing operation with the developer is not required in advance, so the replenished toner mixing / conveying path 64 is blocked and the developer is collected from the developing unit. There is no such thing. As a configuration for this, although not shown, there is a configuration in which an opening / closing member is provided on the developing unit side of the replenishing toner mixing conveyance path 64 so that the developer discharge port in the developing unit can be set in a closed state.

DESCRIPTION OF SYMBOLS 3 Developing apparatus 30 Developing part 40 Developer accommodating part 41 Developer collection path 42 Developer supply path 43 Container 44A Screw member 45A Stirring blade 61 Toner tank 62 Supply toner conveyance path 63 Air pump 63 Supply toner mixing conveyance path P1, P2 Merge position L1, L2 Transport path length

JP 2009-103750 A

Claims (6)

A developing unit for processing a visible image of the electrostatic latent image formed on the latent image carrier with a developer composed of toner and carrier, and a developer supply unit for the developer recovered from the developing unit again. A circulating portion that moves toward the developing portion, and the circulating portion is provided with a receiving portion for storing a part of the developer at a position before reaching the developing portion, and the collected developer is provided in the receiving portion. And a developing device provided with a stirring member that stirs and mixes newly supplied toner.
In addition to the developer flow path leading to the circulation path, the developing unit is provided with a replenishment toner mixing conveyance path connected to a replenishment toner conveyance path that conveys replenishment toner to the circulation path by an air flow . A developing device characterized in that the replenishment toner and the developer from the developing unit are mixed in the replenishing toner conveyance path and conveyed to the accommodating portion of the circulation unit. The developing device according to claim 1,
The toner conveyance speed in the replenishing toner conveyance path is set by using a ratio of air and toner powder to set a speed at which the toner powder can obtain an air flow rate that is less than air. Developing device. The developing device according to claim 1 or 2 ,
The replenishment toner conveyance path has a conveyance path length from a position where the air flow conveyance of the replenishment toner starts to a position where the developer conveyed from the developing unit joins, and the replenishment toner can be sufficiently dispersed in the air. A developing device characterized in that a distance is set . The developing device according to any one of claims 1 to 3,
A developing device characterized in that , as the air flow velocity in the replenishing toner conveyance path , a speed at which an air flow rate in which the developer is less than air is obtained is set by using a ratio of air and developer . The developing device according to claim 1,
The distance through which the developer can be sufficiently dispersed in the air is set as the length of the conveyance path from the position where the developer and the replenishment toner from the developing unit are joined by the air flow to the accommodation unit of the circulation unit. developing apparatus is characterized in that. An image forming apparatus using the developing device according to claim 1.

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